1. Chemistry Goal 9 P HYSICAL AND C HEMICAL C HANGES

2. T WO T YPES OF C HANGES  1. Physical Changes do not change the composition of a substance, only the physical properties.  2. Chemical changes change the composition of a substance. The change results in the formation of one or more new substances with new properties.

3. H OW DO YOU KNOW IF A CHANGE IS PHYSICAL OR CHEMICAL ?  LOOK FOR EVIDENCE OF A PHYSICAL OR CHEMCIAL CHANGE!!

4. E VIDENCE : PHYSICAL CHANGES  Change in the state of matter  When a substance changes from one state of matter to another, the composition of the substance remains the same.  Deposition – when a substance changes directly from a gas to a solid frost  Sublimation – when a substance changes directly from a solid to a gas Dry ice or solid air fresheners

5. E VIDENCE : PHYSICAL CHANGES  Change in size or shape  When a substance changes size or shape, its composition remains the same. Examples:  Tearing/cutting paper  Mowing the grass  Chopping wood  Gluing paper together

6. E VIDENCE : CHEMICAL CHANGES  Color Change:  When a substance changes color, the chemical composition may have changed. Example: Copper turning green  It is possible to have a color change without a chemical change. Adding food coloring to water changes its color but no chemical change has occurred.

7.  Temperature change:  When a substance is combined with another substance, there may be an increase or decrease in temperature. Example: A hand warmer  It is possible to have a temperature change without a chemical change. When you heat water to boil it, the temperature increases but no change in composition occurs so it is not a chemical change. E VIDENCE : CHEMICAL CHANGES

8.  Formation of Precipitate  When two solutions are combined they may form a solid substance. This solid is called a precipitate. It indicates a chemical change has happened.  The precipitate may be in the form of very small particles, which will make the solution look cloudy.

9. E VIDENCE : CHEMICAL CHANGES  Formation of a Gas  When solid or liquid substances are combined, they may form gas bubbles. Example: Baking soda and vinegar  It is possible to form gas without a chemical change. When boiling water, gas bubbles form but there is no change in composition so no chemical change has occurred.

10. C OPY DOWN THE TABLE ON THE BACK OF YOUR NOTES : What changed? What type of change? Evidence? (can be more than one piece of evidence) Tearing Paper Burning Paper